图的邻接表实现（Java）

当图的结点多边少（又称为稀疏图）的时候，相比使用邻接矩阵存储，使用邻接表存储图的空间效率更高。
使用邻接表存储图的时候，图的每个结点对应一个边链表，也就是说，每个结点所包含的边构成一个链表。例如结点A和B相连，A也和C相连，若边e1表示A和B之间的边，e2表示A和C之间的边，那么结点A包含的边链表就是e1->e2，其中e1保存着A的临接点B，e2保存着A的临接点C。

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Graph.java

import java.util.LinkedList;import java.util.Queue;import java.util.Stack;//实现图的邻接表结构class Edge {//边：作为邻接表中每个结点的边链表的元素，例如结点A和B构成边e1，那么A拥有e1，在A的边链表中，e1的verAdj = B    int verAdj;    int weight;    Edge nextEdge;//如果结点A拥有多条边，边构成链表，例如e1->e2->...->en}class Vertex{    int verName;    Edge edgeHead;//边链表的头指针}public class Graph {    private Vertex[] vertexs;    private boolean isDirected;//若为有向图，则isDirected为true    Graph(int[] vexs,int[][] edges,boolean isDirected){//图的初始化        //vexs包含各顶点的编号，若有n个顶点，顶点的编号范围是0~n-1        //edges是一个n×3的数组，，边的权值等于edges[i][2]，若为有向图，那么edges[i][0]指向edges[i][1]        vertexs = new Vertex[vexs.length];        this.isDirected = isDirected;        if(isDirected == false){//无向图的初始化            for (int j = 0; j < vexs.length; j++) {                vertexs[j] = new Vertex();                vertexs[j].verName = vexs[j];                Edge cur = null;                for (int i = 0; i < edges.length; i++) {                    if(edges[i][0] == vexs[j]){                        if(vertexs[j].edgeHead == null){                            vertexs[j].edgeHead = new Edge();                            vertexs[j].edgeHead.verAdj = edges[i][1];                            vertexs[j].edgeHead.weight = edges[i][2];                            cur = vertexs[j].edgeHead;                        }else{                            while(cur.nextEdge != null) cur = cur.nextEdge;                            cur.nextEdge = new Edge();                            cur = cur.nextEdge;                            cur.verAdj = edges[i][1];                            cur.weight = edges[i][2];                        }                       }else if(edges[i][1] == vexs[j]){                        if(vertexs[j].edgeHead == null){                            vertexs[j].edgeHead = new Edge();                            vertexs[j].edgeHead.verAdj = edges[i][0];                            vertexs[j].edgeHead.weight = edges[i][2];                            cur = vertexs[j].edgeHead;                        }else{                            while(cur.nextEdge != null) cur = cur.nextEdge;                            cur.nextEdge = new Edge();                            cur = cur.nextEdge;                            cur.verAdj = edges[i][0];                            cur.weight = edges[i][2];                        }                       }                }            }        }else{//有向图的初始化            for (int j = 0; j < vexs.length; j++) {                vertexs[j] = new Vertex();                vertexs[j].verName = vexs[j];                Edge cur = null;                for (int i = 0; i < edges.length; i++) {                    if(edges[i][0] == vexs[j]){                        if(vertexs[j].edgeHead == null){                            vertexs[j].edgeHead = new Edge();                            vertexs[j].edgeHead.verAdj = edges[i][1];                            vertexs[j].edgeHead.weight = edges[i][2];                            cur = vertexs[j].edgeHead;                        }else{                            while(cur.nextEdge != null) cur = cur.nextEdge;                            cur.nextEdge = new Edge();                            cur = cur.nextEdge;                            cur.verAdj = edges[i][1];                            cur.weight = edges[i][2];                        }                       }                }            }        }    }    void bfs(){//广度优先遍历        if(vertexs == null || vertexs.length == 0) return;        Queue<Vertex> queue = new LinkedList<Vertex>();        boolean[] visited = new boolean[vertexs.length];        for (int i = 0; i < visited.length; i++) {            visited[i] = false;        }        queue.offer(vertexs[0]);        visited[0] = true;        System.out.print(vertexs[0].verName);        while(!queue.isEmpty()){            Vertex v = queue.remove();            Edge e = v.edgeHead;            while(e != null && visited[e.verAdj] == false){                queue.offer(vertexs[e.verAdj]);                visited[e.verAdj] = true;                System.out.print(e.verAdj + " ");                e = e.nextEdge;            }        }    }    void dfsNonRec(){//邻接表非递归深度优先遍历        if(vertexs == null || vertexs.length == 0) return;        boolean[] visited = new boolean[vertexs.length];        for (int i = 0; i < visited.length; i++) {            visited[i] = false;        }        Stack<Vertex> stack = new Stack<Vertex>();        stack.push(vertexs[0]);        visited[0] = true;        while(!stack.isEmpty()){            Vertex v = stack.pop();            visited[v.verName] = true;            System.out.print(v.verName + " ");            Edge e = v.edgeHead;            while(e != null && visited[e.verAdj] != true){                stack.push(vertexs[e.verAdj]);                e = e.nextEdge;            }        }    }    void dfs(){//dfs和dfsRec共同实现邻接表存储的图的递归深度优先遍历        if(vertexs == null || vertexs.length == 0) return;        boolean[] visited = new boolean[vertexs.length];        dfsRec(visited, vertexs[0]);    }    void dfsRec(boolean[] visited,Vertex vertex){        if(vertex == null) return;        visited[vertex.verName] = true;        System.out.print(vertex.verName + " ");        Edge e = vertex.edgeHead;        while(e != null){            if(visited[e.verAdj] != true){                dfsRec(visited, vertexs[e.verAdj]);            }            e = e.nextEdge;        }    }    void printGraph(){        if(isDirected == false){            for (Vertex vertex : vertexs) {                Edge e = vertex.edgeHead;                while(e != null){                    System.out.println(vertex.verName + "--" + e.verAdj + "  weight = " + e.weight);                    e = e.nextEdge;                }            }        }else{            for (Vertex vertex : vertexs) {                Edge e = vertex.edgeHead;                while(e != null){                    System.out.println(vertex.verName + "->" + e.verAdj + "  weight = " + e.weight);                    e = e.nextEdge;                }            }        }           }}

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Main.java

public class Main{     public static void main(String[] args){         int[] vexs = {0,1,2,3,4,5};         int[][] edges = {{0,1,100},{0,2,100},{0,3,100},{1,4,100},{2,5,100},{4,5,100},{5,3,100}};         Graph g = new Graph(vexs, edges,true);         g.bfs();         //g.dfs();         //g.dfsNonRec();     }}